Petroleum wells for the exploitation of oil and/or gas from a reservoir normally consist of an upper and outer conductor, which forms the base of the well, an upper casing arranged into and in extension of the conductor, and further down in the well more casings which are arranged into and overlaps the above casing. A production tubing string is located in the middle of the well for transporting petroleum from the bottom of the well to the earth's surface or to the sea floor. Annuli will then be formed between the different casings.
Several wells will normally be drilled in a reservoir, where some of these are test wells which are only used for a shorter period prior to the production from the reservoir, and thus will be plugged after testing. If a test well is a successful well, such a well will normally be temporary plugged before the production starts, while a test well which is “dry”, i.e. a well in which the hydrocarbon content is too small to be worth producing, will be plugged permanently.
However, as the production from a well gradually falls, all wells will sooner or later have to be abandoned. Before the well is permanently abandoned, the well must be securely plugged, where there are official requirements with respect to how the work is to be carried out and to its completion.
For this purpose normally concrete plugs are used to provide a barrier in the well.
For example, a common requirement during plug and abandonment operations is to have a plug set inside an inner casing string and a further plug set in the annulus between the inner casing string and the outer casing string. The plug will then extend across the full cross sectional area of the well and seal both vertically and horizontally in the well.
In other operations, where setting of a barrier in a well is required, it may be that additional official requirements must be fulfilled.
Other common methods of performing annular sealing during temporary or permanent plugging and abandonment of an oil and/or gas well, all of which have the goal of having the cement placed in the annulus in a secure and safe manner via either holes in the tubular or by directly pumping in the annulus, are as follows: a) so-called shoot and squeeze, which displaces the fluid by use of an open-ended drill pipe or tubing, b) top down cementing, c) circulation squeeze, d) hesitation squeeze.
All of the above methods a)-d) have challenges relating to conforming the cement over the full interval, as it relates both to the placing as well as the logging. The placing of the cement is not conclusive as the cement will have to change place with the annulus fluids present in the annulus prior to placing barrier cement. The fluid which is present in the annulus needs to be evacuated/forced to either above or below the interval or through the formation rock by formation leak-off.
The current logging technologies, e.g. Ultra Sonic Imager Tool (USIT), Cement Bond Log (CBL), Segmented Bond Tool (SBT), have proven very subjective regarding being able to conclusively confirm or verify that the barrier is sealing properly in the annulus. The current designs of today's logging tools are fully dependent on a logging-friendly downhole environment, i.e. the environment needs to fulfill certain demands to be able to perform a proper logging operation.
Document WO 2012/096580 A1 describes a method and washing tool for combined cleaning of an annulus in a well across a longitudinal section of the well, and subsequent plugging of the longitudinal section.
It is, though, a challenge with the solution described in WO 2012/096580 A1, as well as with the other known solutions, that the displacement of the washing fluid by the cement is not satisfactorily. In the worst case, the result is a leaking cement plug. One of the embodiments described in WO 2012/096580 A1 includes dropping of the perforation tool subsequent to the perforation of the well, washing the perforated zone, setting the washing tool at a location in the well, and finally cementing in the perforated zone. Additionally, subsequent to the introduction of the cement, the normally remaining washing fluid that has not been displaced during the cementing operation has to be displaced by pressurizing the cement plug. However, such pressurizing of the cement plug may result in the cement plug not sealing off the well properly, as not only the washing fluid will be forced or squeezed out of the tubular and into the surrounding formation, but also the cement. Furthermore, the cement plug will not be subjected to the same pressure over its length, whereby the cement may not be distributed equally around the periphery of the well.
It is therefore an objective of the present invention to provide a method of plugging a petroleum well permanently or temporary that is more reliable compared with the solutions described in prior art.
More specifically, an objective of the present invention is to provide a solution securing a more reliable and controlled displacement of the fluids, e.g. sealing fluids, present in the annulus in a P&A operation or in other operations where setting of a barrier in the well is required.
Another objective is to provide a method making it possible to perform perforation, washing and cementing in a single trip in the well.
The person skilled in the art will now how to perform the lowering, perforation and washing sequence of the operation. Hence, a detailed description of these operations is not described in the present application. For further information a method including the above mentioned steps (lowering, perforation and washing), e.g. as described in WO 2012/096580 A1, may be applicable in the present invention as well.
The present invention relates to a method of performing a plug and abandonment operation or during other operations where setting of a barrier in the well is required by the use of a multitask tool, for instance a combined perforate and wash tool or just a wash tool, where the tool is used to displace both the washing liquid and the sealing liquid, at least one lower set of sealing arrangement and at least one upper set of sealing arrangement arranged below and above a fluid displacement arrangement, the fluid displacement arrangement comprising a plurality of radial holes, wherein the method comprises the steps of:    a) lowering the tool to the desired location in the well,    b) perforating at least a section of the well if the section is not already perforated,    c) washing said perforated section by pumping washing and/or cleaning fluid through the plurality of radial holes of the displacement arrangement,    d) sealing off a lower portion of the well at a location below the perforated section by the use of the at least one lower set of sealing arrangement,    e) sealing off the well in a lower portion of the perforated section by using the at least one upper set of sealing arrangement,    f) pumping a sealing fluid through the plurality of radial holes of the displacement arrangement,    g) lifting the tool through, and above, the perforated section, while continuing pumping of the sealing fluid.
The lower and upper set of sealing arrangement, being comprised of cups, e.g. swab cups, may comprise one or more individual swab cups for sealing against the surrounding formation, tubular etc.
In an aspect of the preferred embodiment of the invention, the method may further comprise, subsequent to step c), but prior to step d), pulling and lowering the tool for a number of times in the perforated section for performing additional washing of the perforated section.
In an aspect of the preferred embodiment of the invention, the method may further comprise, after step g), a step h) comprising by-passing excess sealing fluid or present annular fluid through a bypass-system bypassing the sealed portions of the well.
In an aspect the bypass-system is arranged in the tool and the sealing fluid or present annular fluid may be lead from the annulus through a second set of openings of the bypass-system, further through the tool and out of a first set of openings of the bypass-system to a location above the sealed portions of the well.
In a preferred embodiment of the method, the tool comprises an internal plugging element, which internal plugging element may be adapted to be activated by means of a remote operation.
In an aspect, the sealing fluid may comprise cement for forming a cement plug. The sealing fluid may also comprise other fluids such as Sandaband®, Thermaset® (Wellcem), Liquid Stone® or similar.
The steps may be performed in a single trip in to the well.
In another embodiment of the method, the steps may be performed in two or more trips in to the well.
In a variation, the washing fluid and the sealing fluid may be pumped through a plurality of radial holes of the displacement arrangement, and the radial holes may be arranged in a spaced-apart relationship around a circumference of the tool.
In a variation, the method may further comprise the step of squeezing present annular fluid or sealing fluid from a location above the sealed portions to a location below the sealed portions in the well by leading the fluids through a first set of openings of a bypass-system above the sealed portions and out of a second set of openings of the bypass-system below the sealed portions.
In a variation, the method may further comprise, after step h), a step i) comprising lifting the tool to a position above the sealing fluid in the well and cleaning the tool by pumping a washing fluid through the tool and the first and second set of openings of the bypass-system.
It shall be clear for the person skilled in the art that the different embodiments and aspects of the invention may be combined in any way, even if they are not explicitly described as one specific embodiment in the described embodiments.